Application Guide - NP900 Series
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A996A
Cables current carrying capacity is mostly depend of the cross section of the conductor
diameter as well as the conductor material. Second most important factor is the insulating
material of the cable and how much it can withstand temperature. As can be seen all
factors except the air temperature are quite stabile especially when the cable is dug deep
enough so that it lies below the ground frost in places where the outside temperature can
go under freezing point. Heat conducting from the cable into the surrounding ground is
directly equal no matter if the cable is heating or cooling and it is defined by the ground
composition how well the ground conducts the heat. However these matters are loading
factors which effect only to the maximum current carrying capacity of the cable and they
are not the time constants of the cable. When considering the time constants the only
constant is the heating time constant and cooling time constant which in the case of
ground dug cable is the same.
Figure 3.3.2-108 Simplified motor construction and time constants.
When looking at normal induction machine like electric motor the following major
components can be found: Rotor, which as the name suggests is rotating and its shaft is
used for power outlet from the motor (drive end), Stator generates the electromagnetic
field which induces into rotor and makes it rotate (thus the name induction motor) and also
the motor body which contains stator and rotor. Motors always have some cooling system.
Most common is in the rotor shaft mounted fan (cooling end) and in bigger motors or slow
rotating motors the cooling may be active with additional fans or with liquid cooling.
By looking at motor thermal properties can be found not just one but several very different
components which all have thermal time constants of their own, rotor has own time
